These are my settings. I chose a fairly low frequency as many digital meters on the AC range will work at audio frequencies.

Select your soundcard and drivers in use.

Connect the Softrock TX input labelled "Line Out" to the computer Line Out.

Connect a power meter and dummy load to the Softrock output.

Power up the Softrock and USB. GFGSRhttp://home.ict.nl/~fredkrom/pe0fko/CFGSR/ may be used to set the frequency to the lowest range covered. The Tune tab has buttons to make band changes quick. AND on the "Test" Tab it has a PTT button.

The Ensemble does not have COM port PTT so you can use a cliplead to ground the top left-hand lead of U4 (Pin 4), activating PTT. Thanks for the pictures Robby! BUT see CFGSR above! http://www.wb5rvz.com/sdr/ensemble/index.htm

TOOLS:- The AC range of many modern digital meters is specified to work at audio frequencies. If you have one of these then it will probably tell you the approximate audio RMS voltage present.

For the RF measurements this can not be used. An oscilloscope or just a simple diode probe will give a good idea of the levels present. The oscilloscope and it's probes will need to be specified to work on the test frequency. A diode probe should cover any HF frequency.

Diode probe example http://www.n5ese.com/rfprobe2.htm (Lots of things on this site!) This will read RMS with a 10M Ohm digital meter. Multiply by 4 if you have a 1M Ohm meter.

Below, my build of one of these.

A piece of copper clad board cut to fit inside a pen shell. Lands made with small saw blade.

Components soldered. A stainless pin or needle may be difficult to tin with solder. A suitable flux may be needed.

Assembled. Not seen is the ground wire and clip that goes to ground on the item under test.

This probe actually has slightly different components and seemed to work better.

It is a single diode probe with a low-value resistor, not critical, 15K used here. It will read PEAK voltage.

A complete unit. This one is an integrating probe, a series 47K resistor followed by a 0.1uF to ground. The red clip is the ground connector, I'd run out of black sleeves! This may be used for measuring DC voltages where RF is present, like on the Softrock divider and mixer.

AUDIO FREQUENCY TESTS

Set IQout "Volume" to a low setting, start it and enable PTT. Gradually increase this level until 500mW (1/2 watt) output is achieved. 500mW is 5V0 RMS, 7V1 peak measured at the antenna terminal with the dummy load in place. If this is not reached I hope the measurements will give a clue where to look! Note:- Do not exceed an audio input level of 0.7 volts RMS.

Set the audio to 0.5 volts RMS and see where they vary greatly from mine, below.

I have taken the schematic from Robby's SDR site. http://www.wb5rvz.com/sdr/ The red dots show where the exposed "hairpin" of the resistors are.

Audio voltages may be measured at the hairpins of R26, 25, 28, and 27.

For 500mW out I measured about 1V2 peak-peak on an oscilloscope and about 0V5 RMS with a digital meter.

Voltages at pin 2 and at the audio inputs will be similar.

If the input voltage is lower than this then check the soundcard mixer settings.

Some cards will go much higher,

March 2015:- Note tests done by Warren, 9V1TD indicate that to conform with FCC spurious emission requirements this level should never be increased above 0.7 volts RMS. If 1/2 to 1 watt output is not obtained then it is likely there is something wrong. For the 15/12/10 metre versions more drive may be used, the spurious signal is in fact lower at higher frequencies.

RF CHECKS

With an oscilloscope:- Voltages PEAK TO PEAK. Make sure the oscilloscope and probes are specified for the frequency used. Frequencies higher than this may be used but sensitivity will be less and readings lower.

Normally a x10 probe will be used to obtain the specified frequency response. Check your measurements using the scopes "Calibrate" signal or put it to DC input and check the 5V line or a battery to be sure you are reading correctly.

Transformers will show a reading on three of the six connections, at one end of each winding..

One of my diode probes measures approximate PEAK voltage the other RMS. [RMS probe 0.7 times lower voltage. These RMS voltages were confirmed using a Bradley RF voltmeter with an unterminated probe] I found my RMS diode probe gave unreliable results at T2 where voltages are low.

Tests at 3.5MHz.

Test Point

Oscilloscope Peak to Peak

Probe PEAK Reading

Probe RMS Reading

Each End of T2 Primary. (R30,31)

0V4

0V3

0V2

T2 Secondary (C20/L1)

0V6

0V3

0V3

Junction of L1 and C21

1V0

0V5

0V4

Q6 Emitter and Base

0V8

0V5

0V4

Q6 Collector

4V0

2V6

1V9

T3 Primary (R44 hairpin, same as Q6 collector)

4V0

2V4

1V9

Each end of T3 Secondary. (Q7,8 Gate)

2V0

0V6

0V7

Each End of T4 Primary (Q7,8 Drain)

6V5

4V1

3V0

T4 Secondary

8V0

5V1

Antenna (With 50 Ohm Load)

6V5

3V6

These points are easily identified underneath the board, not so easy from the top but at least some of them are accessible. You do not need ALL these measurements.

All measurements need a fine probe and care must be taken not to slip and short two points together.

NOTE Some of these readings do not seem consistent. Take them as approximate. The important thing is that they should increase as you progress through the transmitter.

I did some tests on my Softrock 6.3, which is really the
same as an Ensemble but with plug-in coils. This seems to show that the Softrock
TX is limited on the high bands.

These are derived from the amount of drive required using WSPR. This
has a drive control calibrated in dB which seems reasonably close. (I measured
-29db over it's range of -30dB, most likely the 1dB difference is my
error.)

Using a fixed audio level I recorded the following WSPR attenuator values.

1 Watt out on 80/40m

-11dB

1 Watt out on 15m

-8dB This was the 1dB compression point

1 Watt out on 12m

-5dB

1 Watt out on 10m

-1dB The 1dB compression point was at 500mW so 1 watt required an extra 8dB.

I measured at the equivalent points below. Again the measurements from the probe, probably a different one than used above, do not match the scope readings at low voltages.

Test at 28MHz.

Test Point

Oscilloscope Peak to Peak

Probe PEAK Reading

Each End of T2 Primary. (R30,31)

0V7

0V6

T2 Secondary (C20/L1)

1V4

1V6

Junction of L1 and C21

Q6 Emitter and Base

2V0

1V6

Q6 Collector

5V0

2V8

T3 Primary (R44 hairpin, same as Q6 collector)

Each end of T3 Secondary. (Q7,8 Gate)

3V0

1V4

Each End of T4 Primary (Q7,8 Drain)

8V0

4V9

T4 Secondary

11V0

5V4

Antenna (With 50 Ohm Load)

12V0

6V3

Driven to about 500mW on 28MHz. The audio drive was 1V8 peak to peak on the scope. This is only just below the 0.7 volts RMS maximum allowable figure.

You will realise that a diode probe is ideal for setting low TX powers. One may be made with the addition of a 50 Ohm load with a coax lead for the Softrock output. The dummy load may just be a 1/2 watt 50 Ohm resistor or a parallel combination. Even 4 off 220 Ohms and a 560 Ohm in parallel would suffice.

My method of checking the 1dB compression point.

This is a test to determine the maximum linear output of an amplifier. An oscilloscope will not show small levels of distortion.

I measure the RF output across a 50 Ohm load reasonably accurately. I use an old Bradley RF meter, convert to dB.

A diode detector, like the probe above should measure PEAK RF voltage with a 10M Ohm meter. But check this. Calibration may still be necessary.

Using something like IQGen (see above) I increase the drive dB by dB. As power increases there will come a time when the output does not rise a whole dB. When the RF output lags the input by 1 dB then that's the 1dB point.

This occurs at something like 1 watt on some low bands on some of my RXTXs but not that much in the mid-high bands.

Then a scope may be used to check the level. Do not exceed this level for linear modes like SSB, PSK.

To get a rough check of whether a soundcard SDR receiver is working connect phones to the output of it. Tuning
through a busy band should produce some high pitched noises that may
well sound something like radio signals. Stereo phones should reproduce
sound in both channels. If your ears are old this needs care! The high
frequencies may not be heard, or maybe just in one ear. Use a good antenna. Ensure the band is "open".

If you have now found the SDR is not functioning properly then fault-finding will be required.

If it is a Softrock see if Robby lists it here http://www.wb5rvz.com/sdr/ go
through the various checks. Commonly faults are due to bad solder
joints, bridges or solder splashes. Check with an eyeglass. Sometimes
component values are confused. Check ICs are the correct way round.
Resistors should be measured before fitting. A fault causing no reception on RX/TX
Softrocks can be due to faulty BS170s, used as switches in the antenna
changeover. Bob's drawing of the switching in the PDF. http://groups.yahoo.com/group/softrock40/files/G8VOI/ Ensemble RXTX PTT fault finding.

One way of testing can be to lift the end of L4 that goes to Q10 Q11. Connect the antenna to the free end.

Transmit output. To avoid any software an initial very basic check could be to feed audio to the Softrock's socket labelled "Line Output". Using the PTT method described at the top of this page two RF signals should be produced. Two signals because the audio will not be IQ, 90° separated.

A minimum of a general purpose TEST METER for
voltage, current and resistance is required. Most will use a digital
meter. Be aware that some readings will vary between different
Softrocks. Readings made where square waves are present, on the dividers
and mixer, may vary a lot.

METER PROBES. Use great care. Do
not short out anything when testing a live circuit. Use suitable small
tipped probes. Ensure the meter is on the correct range. Current ranges
in particular should not be used for testing when voltage measurements
are required.

Also, a GENERAL COVERAGE RECEIVER may help to diagnose and confirm operation.

A
pin held in your fingers can act as an audio generator. Test the
Ensemble RX op-amp:- just touch pins 2 and 6 of the audio amp U11 with a
pin. The
SDR display will show the effect and you will hear a hum if you tune to
the centre. If nothing is found check by touching the pins of the "Line
In" jack.

Also, try U10. Pins 2,4,5,7,9,10,13,14 also produce a hum. This is a rough test of U10 and the components after it.

OSCILLOSCOPE Robby's
construction tests shows the use of an oscilloscope. I do not consider
this essential. Indeed unless you are experienced in interpreting what
you see they can obstruct progress. Recently someone showed a superb
oscilloscope picture of a faulty transmit signal. It was three weeks
before someone interpreted it correctly. In the meantime a few simple
checks would quickly have pointed to the faulty audio cable.

Very occasionally a scope may help.

TEST EQUIPMENT FOR TRANSMITTERS.

A METER. Note the "PA
Standing Current" test can give larger variations than quoted in
Robby's pages. This is not considered significant. The specification for
these FETs gives a large tolerance for this value.

A RECEIVER IS ESSENTIAL in order to setup the image rejection. With SDR transmitters this is always a manual adjustment.